By default the libraries will be downloaded and installed into
C:\wireshark-win32-libs.
You can change this to any other location by editing the file
config.nmake and changing the line containing
the WIRESHARK_LIBS setting to your favourite place (use an absolute path
here).

5.3.2. Update of a previous download

As new versions of the libraries become available, maybe with bugfixes or
some new functionality, your libraries get outdated.

You could simply remove everything in the WIRESHARK_LIBS dir and call the
setup target again, but that would require a download of every file again,
which isn't necessary.

The following will bring your libraries up to date:

Update your Wireshark sources to the latest SVN files (see Section 3.3, “Obtain the Wireshark sources”), so the zip filenames in the setup target
of Makefile.nmake are in sync with the library zip files on the server.

Execute the library setup command as described above.

>nmake -f Makefile.nmake setup

Note that this command will automatically do a clean-setup which will
remove all files previously unzipped from the downloaded files in your
WIRESHARK_LIBS library path (all the subdirs, e.g.
c:\wireshark-win32-libs\gtk+),
except for the zip files located at the toplevel, which are the files
downloaded the last time(s).

Also note that as wget will download only the
missing (updated) files, existing zip files in the WIRESHARK_LIBS dir won't be
downloaded again. Remaining (outdated) zip files shouldn't do any harm.